The invention relates to an ultrasonic tomograph operating according to transmission, scattering and impulse echo methods for the examination of tissue of extremities particular the female breast tissue and the male reproduction organs.
In medical engineering, ultrasound examinations become increasingly important. At one hand, in contrast to X-radiation ultrasound does not damage the tissue being examined. On the other hand, tissue types can be distinguished by ultrasound imaging which, with other imaging procedures such as x-ray examination, provide for only very little contrast.
A medical ultrasonic apparatus consists essentially of an ultrasound head with a number of ultrasound transducers as well as a control unit and an evaluation unit which emits the control impulses for the ultrasound transducers and which receives the measuring signals obtained from the transducers as electrical signals. The electrical signals are amplified by the control unit and, during the measuring procedure, reconstructed on a screen for real-time imaging. The complexity of such a reconstruction in real time limits not only the number of individual transducers employed with such ultrasonic apparatus but also to a great extent the correction capabilities during the reconstruction. Furthermore, the ultrasonic heads are generally not stationary but are manually moved. These facts substantially limit the capabilities during examinations with contrast media in ultrasound mammography where high spatial and time resolution is very important for the reconstruction. An additional limitation is an insufficient reproducibility.
U.S. Pat. No. 4,478,083 discloses a system for ultrasound mammography using the impulse-echo procedure wherein the female breast is inserted in a suitable manner from the top into a cylindrical container and positioned therein. Ultrasonic transducers are uniformly distributed over the whole cylindrical wall surface of this container. It can be assumed that the main radiation emission direction of each ultrasonic transducer is normal to the container wall into the container interior (see column 5, last par.). For the composition of a three-dimensional image of the breast being examined, an evaluation unit is described with a circuit so designed that various areas of the breast are first defined and then successively subjected to the ultrasound. To this end, for each impulse-echo procedure, only a single transducer or group of ultrasound transducers is energized for the emission of the ultrasound impulse and also for the reception of the returning sound echo by means of an electronic switch. The returning sound echo is filtered out by the determination of time windows.
DE 28 27 423 A1 discloses an apparatus for the determination of the internal structure of a body by means of sound radiation wherein a body is immersed in a container filled with a coupling medium and is subjected to ultrasound in this container. In this procedure, a sound beam is directed from one or several ultrasonic transducers through the body to at least one ultrasonic transducer serving as a receiver. The received signals are electronically processed in an evaluation unit, are stored and then the distribution of the sound refraction index and of the absorption coefficient are determined. In parallel therewith in the evaluation unit, using a point raster, a model of the body is composed which can be optimized by iterative sound measurements and which can be processed to individual cross-section images.
In a particular proposed embodiment, the sound transducers in the container are arranged in a matrix in the form of a cylinder. In that arrangement, a limited number of transducers must be activated as senders and also as receivers by an electronic switch wherein, for each active receiver, a subsequent amplifier, possibly with additional electronic stages (see page 24, paragraph 2), is provided. With this arrangement, transmission and scattering components and also echo components of the ultrasonic impulses can be received but they are not utilized for evaluation.
In a similar way, in the ultrasound apparatus disclosed in U.S. Pat. No. 5,673,697, a body is arranged in a container with ultrasonic transducers firmly mounted over the whole wall structure of the body and is exposed to ultrasound from at least one of those transducers with an ultrasound frequency of 1 to 5 MHz. All the other transducers can be employed successively by an electronic switch as receivers, whose signals are successively amplified for further processing and recorded. For the further processing the travel time, the phase and amplitude of the received ultrasound impulses are employed. By way of the reflection properties and sound speeds determined therefrom a three-dimensional image of the body is generated. The system however is not suitable for a reconstruction of rapid movements, since the time-delayed (non-simultaneous) recording of the receivers limits the time resolution to a large extent. Consequently, this publication does not provide any hint for a possible reconstruction of time-dependent changes in the body on a real-time basis.
It is the object of the present invention to provide a high-resolution ultrasonic tomograph, which provides for an improved resolution in the reconstruction of three-dimensional images in real time and with high image accuracy.
In a high resolution ultrasonic tomograph operating according to transmission, scattering and impulse-echo methods, comprising a container with an open top and including ultrasonic transducers arranged along the walls of the container, a coupling medium disposed in the container and a computer-based control and evaluation unit with a working memory, the control and evaluation unit is connected in a circuit with the ultrasonic transducers in such a way that the ultrasonic signal emitted from at least one ultrasonic transducer forms an ultrasonic impulse which is received by all the other transducers in parallel and is amplified, filtered and digitized to form electric signals which are stored in the working memory as a data set.
With such an ultrasound tomograph, for example in mammography, dynamic contrast medium examinations permit the reconstruction and evaluation of the female breast with very high time and spatial resolution.
The high-resolution ultrasound tomograph according to the invention will be described below in greater detail on the basis of the accompanying drawings.